2apples (Fuji, Granny Smith, or any other crisp apple)
Preheat oven to 225F.
Slice apples as thinly as you can with a very sharp knife or a mandolin. (Cut the apple horizontally, so the core goes through each slice.) *You can core the apple first, which might be more practical but also much less pretty.
Place apple slices on a parchment-lined baking tray, making sure there are no overlapping pieces, and sprinkle with cinnamon and sugar.
Bake for 1 hour. Take out of the oven, flip all of the slices, and bake for one more hour.
Turn the oven off after the second hour, but leave apple slices in until they’ve cooled and crisped.
Enjoy immediately or store in an airtight jar for a few days.